Amplifier and oscillator circuit



April 20, 1948. R. J. DAVIS AMPLIFIER AND OSCILLATOR CIRCUIT Filed oct.29, 1943 Patented Apr. 2O, 1948 AMPLIFER AND osoILLAToR cIncUrr Robert J.o Davis,y Luthervlle, Mtl., assigno'r to Bendix Aviation Corporation,VNew York, N. Y., a

corporation of Delaware Application October' 29, 1943, Serial No.508,177'

13 Claims. (Cl. Z50-17) v This invention relates to. vacuum tube signalamplifiers and more particularly tol vacuum tube signal amplifiers whichmay be optionally employed as generators of alternating current energy.

Present day radiotransmitters are normally designed to emit a number ofdifferentl types of radiation, among which are: voice modulatedcontinuous waves, keyed continuous waves and keyed continuous waves witha steady modulation tone impressed. The generation of waves ofthe thirdtype requires that a steady audio tone, be. generated within theequipment which is then utilized to modulate. the transmittedl energy.This is usually accomplished by the use of a separate oscillator tubegenerating the desired frequency which is set into operation andconnected to the modulating amplifier when keyed MCW, as the third typeof. radiation is often designated, is to be transmitted. During periodsof Voice modulated transmission, the modulating oscillator isdeenergized and thefmodulating ampliiier is actuated by voice currentsfrom the speech amplifier. In some cases, the modulating,

frequency is generated by disconnecting the speech amplifying ormodulator tubes fromttheir normal circuits and connecting them to a newset of circuit components arranged to provide sustained oscillations. Ineach of the above instances, the provisions made for generating thetonemodulation frequency have added materially to the bulk, expense,and/or weight of the equipment as it has been necessary to provideadditional tubes and circuit components,

One of the principal objects of this invention is to provide new andnovel means for optionally utilizing a signal ampliiier as anoscillation generator.

Another object of the invention is to provide new and novel means foroptionally utilizing a vacuum tube as a degenerative signal amplifierand as an oscillation generator.

Still another object of the invention is to provide a radio transmittercapable of emitting both voice modulated continuous waves and keyed MCWhaving less bulk and Weight than existing apparatus of this type.

TheA above objects and advantages of the invention are accomplished byproviding means forV selectively impressing energy from the outputcircuit of a vacuum tube ampliiier on thek input circuit of the sameamplifier with a positive or negative feedback relationship. Thepositive feedback is of a magnitude producing sustained(- oscillationswhose frequency may be controlled 2v by a tuned circuit simultaneouslyconnected in the output circuit or in-putY circuit of the ampliiiertube; and the negative feedback reduces. the amount of distortionlproduced in the amplica.- tion process in the well known manner whenothetube is. acting as a signal amplier.

Other objects and advantages will in part be disclosed and' inpart beobvious when the following speciiication is read in conjunction with thedrawing which. is a schematic diagram of a transmitter modulator unitincorporating the in,-

vention. r

Referring to the drawing, the control grid ll ofthe speech amplifier 2is connected to ground through the gridleak, resistor 55 and to a sourceof voice currentsas. indicated. Energy from this source is applied tothe speech ampliiier only when. it l isv desired to transmit voicemodulated. ca ;rriier waves. Theanode 3 of amplifier 2l is. connectedthroughv theY anode load 'resister 5i to a contactll' of the switchsection di, and an arin 16, which is a part ofthe same switch section isconnected to the positive terminal ofthe intermediate voltage source 4and is selectively mov'- able between the contact. 84 and a secondcontact 13; The source 4 may supply adirect current po tential of 380volts. The anode circuit of tube 2 is completed by the cormectionl ofthe negative terminal or the source 4 directly to ground, and theIconnection of the cathode 6 to ground through the paralleli combinationof resistance 8 and capacity 9 to supply operating bias for the controlgrid i; A heater l elevates the temperature ofY cathode 6` as requiredfor functioning of the tube 2. The heater energizing circuits for thisand the remainder of the thermionic tubes in the apparatus will bedescribed in detail inA a later paragraph.

The anode terminal of the resistor 5 is coupled by the capacitor I3 tothe control grid ll of the oscillator and driver tube l2', here shown tobe ofthe tetrode type,V and a grid resistor lli isconnected'between thecontrol grid il and the mov-n able arm 25 of the switch section 2%,selectively engageable with the contacts liti and 61'. Accelerating grid20 of the amplifier i2 is excited from the sourcer throughl droppingresistor 85 and the contacts l5, I8v ofv the keying relay I9, while theanode I4 of this amplifier is connected with the source A through theprimary I6 ofthe transformer I l. Connected iny parallel between grid 20and ground are the bl'eeder resistor 86` and bypass capacitor 35 toprovide for' adjustment of the' direct grid current voltage andgrounding'for alternating-currents. The cathode 3 2| is connected toground through the resistor 23 and capacitor 24.

A resistive voltage dividing assembly 68, 69 is connected between theanode I4 and ground inseries with the blocking capacitor 10, and theungrounded terminal of the grounded resistor 69, junction .point isattached to the terminal 61 of switch section 26. The values of theresistors 63, 69 are selected to be large as compared with the impedancepresented by the transformer I1, and the voltages appearing at theresistor junction point |00 are substantially 180 degrees out of phasewith the voltages impressed on the control grid Anode I4 is additionallyconnected to the terminal 13 of switch section 6I by the parallelcircuit of inductance 1I and capacity 12, which are selected to beresonant at some desired frequency in the audio spectrum, usuallyapproximately 1,000 cycles per second. This circuit determines thefrequency at which the carrier is modulated when Vmodulated continuouswave transmission is employed.

The output energy from the amplifier I2 isimpressed on the transformerI1 having the center tapped secondary winding 21, whose outer terminalsare connected individually to the control grids 28, 29 of the amplifiers30, 3|. The anodes 36, 31 of these ampliers are connected to the outerterminals of the center tapped primary Winding 38 of the modulationtransformer 39 and the center tap 'of this winding is directly connectedto the positive terminal of source 4. Excitation for the acceleratinggrids 40, 4| of the amplifiers 30, 3| isv derived from the source 4 inseries with the dropping resistor 18, and these grids are also connectedto ground by the bleeder resistor 19 paralleled by capacitor, whoseimpedance is negligible at the operating frequencies. The exact valuesof the accelerating grid supply resistors are determined by the Voltageof source 4 and the characteristics of the particular tube employed.Electron emission for the tubes 30, 3| is provided by the cathodes 32,33 located adjacent the heaters 8|, 82, respectively, and the cathodesare connected to the positive terminal of the heater 82, which is alsoconnected to the positive terminal of the 28 volt source 62 through thefilament dropping resistor 34. As the center tap of the winding 21 andtheA negative terminal of the source 62 are grounded, this connectionprovides the necessary bias for the control grids 28, 29. The two tubes30, 3| serve as the conventional push-pull power amplifier deliveringthe necessary power to modulate the final amplifier stage of the radiofrequency amplifier.

One of the terminals of the winding 21 of transformer I1 is connected bythe blocking capacitor 83 and the resistors 9| and 92 in series to thecathode 2| of amplifier I2, and the potential at the junction point |02of the two resistors is impressed on the contact 66 of the switchsection 26. The connection of this combination to the winding 21 isselected to provide at contact 63 potentials which are substantially inphase with alternating current potentials impressed on the control gridI, and the magnitude 0f the resistors is chosen to provide negligibleloading of the secondary 21. The low potential end of resistor 9| may beconsidered at ground potential for alternating currents because of thebypassing action of capacitor 24, but is above ground potential fordirect current because of its connection to the cathode 2 I.

Located in the transmitter, and excited byV aV radio frequency sourcenot shown in the drawings, is the final radio frequency power ampliiier90. The radio frequency energy from the driver is coupled to the controlgrid 93 by the capacitor 44, and the resulting flow of grid currentthrough resistor 43, connected in series with the choke 42 between grid93 and ground, provides the operating bias. Choke 42 prevents excessiveloss of radio frequency driving power to the resistor 43. Electronemission for the amplifier is provided by the filament 46 having oneterrninal connected to ground and the other connected to the terminalsof the heaters 25 and 8| marked A. The heater and filament circuits thuscomprise heaters 1 and 25 in series, connectedin parallel with heaters8| and B2 in series, which series-parallel combination is then connectedto the source 62 in series with the dropping resistor 34 and the poweramplifier lament 45.

Direct current excitation for the accelerating grid 41 is supplied fromthe source 4 through the keyed contacts l5, I8, secondary winding 49 ofthe modulation transformer 39, and a dropping resistor 48 whose grid endis connected to ground through capacitor 50 to insure the necessaryshielding efciency for stable amplification. The grid 45 of the tubelshown in the diagram is a suppressor grid and is connected to ground forfurther improving internal shielding and diminishing secondary emissioneffects. The anode 5| is provided with power from the high voltagesource 52, which may have a, potential of 1000 volts, by connectionthrough the output choke 53, lter choke 54 and the secondary winding 59of the modulation transformer 39. The eciency of choke 54 in eliminatingradio frequency potentials from the winding 59 is improved by theconnection of the capacitor 60 between the junction of chokes 53 and 54and ground. The radio frequency power existing in the output circuit ofthe amplifier 90 is conveyed to the radiating antenna 'I5 by theblocking capacitor 11 and the variable loading inductor 16, which isvaried to neutralize the residual reactance of the antenna proper.

I-t may be seen by inspection that amplifiers I 2 and 90 are operativeonly when contacts I5 and I3 are in the closed position, as they arewhen the winding of keying relay vI9 is energized. Operation of thisrelay may be controlled by the key 63 connected between the positiveterminal of source 62 and the ungrounded terminal of the operatingwinding for relay I9. Since it is desired to have ampliers I2 and 90continuously in operational uring telephone transmission, a switchsection 60 is provided, having the arm 65 and contact 64 connected tothe respective terminals of the key 63. During the time that switchsection 60 is in the closed position, the operating Winding of relay I9is continuously excited, thereby maintaining amplifiers I2 and 90 in thedesired continuously energized state. As shown in the diagram, switchsections 26, 60 and 6I vare mechanicallycoupled by the member 81, andthe switch sections are therefore simultaneously moveable. The compositeswitch thus formed may be termed the emission selector switch, as itsposition determines the type of intelligence radiated by the apparatus.When in the right hand position, the circuits are those required for the'production of keyed modulated continuous waves, while with the emissionselector switch in the left hand position, the circuit arrangement isthat necessary for the radiation of telephonie signals. The operation ofthe switch assembly may` be readily visualized from the Code-Phonemarkings in the` drawing.

VWith the foregoing in mind, the opera-tion of the apparatus may now bereadily understood. AssumingY the emission selector in the Codeposition, the anode circuit for amplifier 2 isbroken at the contact 84,thereby disabling the telephone input system, andthe arm M is inengagement with the contact 13, thereby connecting the. tuned circuit H,I2 in shunt with the primary I6 ofl the transformer H. Simultaneously,the cathode end of the grid resistor lI!! is connected tothe tap- I-2 onthe. voltage dividerv 9 l, 92A by the switch sectionV 2,l coupling anodecircuit disturbances. of the amplifier I2 back to the control grid II inaiding relationship to an extent causing the tube I2 act asanindependent generator of oscillations when accelerating grid voltageis supplied. Optimum voltage conditions for oscillation Vare secured; bythe connection of the voltage divider to. the cathode 2l,v which removesfrom the grid Il the potentialgenerated by the how of anode currentthrough the cathode bias resistor 23 and allows the control grid toassume an optimum value of bias, generated by the now of gridA currentthrough the grid resistor It which now functions in the same manner asthe grid leak in conventional oscillator arrangements, and the frequencyof oscillation is determined by the insertion of; the resonant circuit1l, 12, peaking the transmission gain at its resonant frequency. As isWell known, the oscillation frequency is that frequency at which thenecessary phase relationships are obtained and the loop circuit gain is.maximum.

In the' Code position of the emission selector, switch section 6Dpresents an open circuit, so that contacts I5, I8 of the keying relayIS. are open except for those intervals when the key 63 is vdepressed;With key 63 down, relay I9`is energized to; close the contacts I5; IBand connect the grid 201 to the source 4, whereupon tube l2 oscillates.During transmission, this oscillation exists in termittently,corresponding to the manipulation of the key 63, Considering the keycondition for the moment, audio frequency oscillation energy from thetube I2 appears across the secondary 21 of.v thel transformer I:'I andis amplified in the usual manner by the tubes 30, 3l to provide in theoutput circuit thereof energy of the same frequency, but materiallyincreased in power. This power is now used to vary or modulate the anodeand screen potentials of the radio frequency amplifier 9U, thusamplitude-modulating the radio frequency energy radiated from theantenna 15. Impression of the modulating energy on both the anode andscreen has been found to effect a material improvement in the linearityof themodulation characteristic. It will be noted that grid 4T alsoderives its power from the source 4 through the contacts of relay I9, sothat with key 63 up, radiation of high frequency energy ceases togetherwith the interruption of the modulating. oscillations.

Upon placing the emission selector switch in the Phone-position, theamplifier 2 is connected to its source of anode potential, and at thesame time, the resonant peaking circuit is disconnected from itsshunting position across the primary of transformer I1, restoring tothis stage its normal uniformity of frequency response. Also, thecathode end of grid resistor I0A is disconnected` from the point |02 andconnected instead to the point |00, which causes anode circuitdisturbances of the tube l2 to appear in the control grid circuit, inopposing relationship` to.

provide degeneration or negative feedback; thereby improving thelinearity of the amplifier response. As resistor 69 is connected toground. there is now provided for the control grid II a negativeoperating bias equal in. magnitude to the voltage drop across thecathode resistor 23 to fulfill the requisites for the faithfulreproduction of the input wave form. Switch section 6u is moved into theclosed position during this operation and shunts the key 63 to maintainthe relay I9; in the energized position continuously.

Under this condition of operation, amplifier 2, functioning. in, theconventional manner, impresses on control grid Il an enlarged replica ofthe wave present at grid I, and this is, in turn, further amplified bythe tube I2 with the excellence of linearity contributed by the presenceof negative feedback, and fed to the modulators 39, 3 I. The output ofthese modulators is impressed, as before, on the iinal radio frequencyamplifier 90, and provides a carrier amplitude modulated with thewaveform of the original telephone or voice frequency input, whichenergy may then be radiated in the usual manner.

While this circuit,. which may be alternatively employed as an amplierand oscillator with the same elements at all times connected to theelectrodes of the tube, has been described in conjunction with radiotransmitting equipment and shown in use as a tone modulator, it will berecognized that its employment is of equal value in any apparatus wherethe alternate functions of signal amplification and the generation of asustained wave ofl predetermined frequency are required.

It will be obvious that many changes and modications may be made in theinvention without departing from the spirit thereof as expressed in theforegoing description.

I claim:

1. In signal responsive apparatus, an electric discharge -device havinginput and output circuits, means for selectively feeding back energyfrom said output circuit to said input ycircuit in phase with and inphase opposition with the energy in saidV input circuit, and means forpeaking the response of said output circuit at a predeterminedvfrequency when the output energy is fed back with an in phaserelationship and eliminating said peaked response when the output energyis fed back in phase opposition.

2. In signal responsive apparatus, an electric discharge device havinginput and output cir cuits, means for selectively feeding back energyfrom said output circuit to said input circuit in phase with and inphase opposition with the energy in said input circuit, said in phasefeedback being of a magnitude sufficient to cause sustained oscillationsin said input and output circuits, and means for peaking the response ofsaid output circuit at a predetermined frequency when the output energyis fed back with an in phase relationship and eliminating said peakedresponse when the output energy is fed back in phase opposition.

3. In signal responsive apparatus, an electric discharge device having acathode, a control grid and an anode, means for impressing input energyon said control grid, a load impedance connected to said anode, a sourceof direct current energy connected between said rcathode and the end ofsaid load impedance remote from said anode, means for impressing afraction of the alternating voltage between said anode and said cathodeon a contact member, means for impressing a fraction of the alternatingvoltage between said anode and said cathode on a second contact memberwith a phase substantially opposite to the phase of the voltage on saidrst mentioned contact member, a third contact member selectivelyengageable with said rst mentioned and said second mentioned contactmembers, an impedance connected between said control grid and said thirdmentioned contact member, a ycircuit comprising parallel inductance andcapacity, and means for connecting said circuit across said anode loadimpedance during the engagement of said second mentioned contact memberby said third mentioned contact member and for disconnecting oneterminal of said circuit from said anode load impedance during theengagement of said rst mentioned contact member by said third mentionedcontact member.

4. In radio transmitting apparatus, an amplifier tube having a cathode,a -control grid and an anode, a transformer having primary and secondarywindings, a connection between said primary winding and said anode, aresistive impedance connected to said anode and to ground, means forimpressing a portion of the voltage across said resistive impedance on acontact member, means connecting one terminal of said secondary windingto ground, a resistive impedance connected between a second terminal ofsaid secondary winding and ground, means for impressing a portion of thevoltage across said second mentioned resistive impedance on a secon-dcontact member, a third contact member selectively engageable with saidfirst mentioned contact member and said second mentioned contact member,a resistive impedance connected between sai-d control grid and saidthird mentioned contact member, a parallel circuit 'of inductance andcapacity resonant to a predetermined frequency, and means for connectingsaid parallel circuit in parallel with said primary winding when saidthird mentioned Contact member is in engagement with said secondmentioned contact member.

5. In radio transmitting apparatus, an amplier tube having a cathode, acontrol grid, an accelerating grid and an anode, a transformer havingprimary and secondary windings, a connection between said primarywinding and said anode,

a resistive impedance connected to said anode and f to ground, means forimpressing a portion of the voltage across said resistive impedance on acontact member, means connecting one terminal of said secondary windingto ground, a resistive impedance connected between a second terminal ofsaid secondary winding and ground, means for impressing a portion of thevoltage across said second mentioned resistive impedance on a secondcontact member, a third contact member selectively engageable with saidrst mentioned contact member and said second mentioned contact member, aresistive impedance connected between said control grid and said thirdmentioned contact member, a parallel circuit of inductance and capacityresonant to a predetermined frequency, means for connecting saidparallel circuit in shunt with said primary winding when said thirdmentioned contact member is in engagement with said second mentionedcontact member, a source of direct current potential having positive andnegative terminals, means connecting said negative terminal to saidcathode, means connecting said positive terminal to the end of saidprimary winding remote from said anode, relay means connecting saidaccelerating 8 grid to said positive terminal, and keying meanscontrolling the operation of said relay means.

6. In radio transmitting apparatus, an ampliiler tube having a cathode,a control grid, an ac'- celerating grid and an anode, a transformerhaving primary and secondary windings, a connection between said primarywinding and said anode, a resistive impedance connected to said anodeand to ground, means for impressing a portion of the voltage across saidresistive impedance on a contact member, means connecting one terminalof said secondary winding to ground, a resistive impedance connectedbetween a second terminal of said secondary winding and ground, meansfor impressing a portion of the voltage across said second mentionedresistive impedance on a second contact member, a third contact memberselectively engageable with the said first mentioned `contact member andsaid second mentioned contact member, a resistive impedance connectedbetween said control grid and said third mentioned contact member, aparallel circuit of inductance and capacity resonant to a predeterminedfrequency, means for connecting said parallel circuit in shunt with saidprimary winding when said third mentioned contact member is inengagement With said second mentioned contact member, a `direct currentsource having positive and negative terminals, means lconnecting saidnegative terminal to said cathode, means connecting said positiveterminal to the end of said primary winding remote from said anode,relay means connecting said positive terminal to said accelerating grid,keying means controlling the operation of said relay means, and meansfor disabling and keying means when said third memtioned contact is inengagement with said iirst mentioned contact.

7. In signal responsive apparatus, an electric discharge device having acathode, a -control grid and an anode, a transformer having primary andsecondary windings, a connection between said primary winding and saidanode, a direct current source having positive and negative terminals, aresistor connecting said cathode and said negative terminal, meansconnecting said positive terminal to the end of said primary windingremote from said anode, a resistive voltage divider connected to saidnegative terminal and connected to said anode by a capacitor, meansconnecting an intermediate point on said voltage divider to a contactmember, a second resistive voltage divider connected to said secondarywinding and connected directly to said cathode, means connecting anintermediate point on said second voltage divider to a second contactmember, a third contact member selectively engageable with said firstmentioned contact member and said second mentioned contact member, and aresistive impedance connected between said control grid and said thirdmentioned contact member.

8. In signal responsive apparatus, an electric discharge device havinginput and output circuits including a plurality of electrodes, animpedance connected at one end to said input circuit, means for applyingelectric potentials to said electrodes,` means for selectivelyimpressing energy from said output circuit on the other end of saidimpedance in aiding and opposing phase relationship with respect to theenergy in said input circuit, and means for varying the potentialapplied to one of said electrodes from one value when said energy iscou-pled back in aiding relationship to another value when said energyis coupled back Vin opposing relationship 9. In signal responsiveapparatus, an electric discharge device having input and output circuitsincluding a plurality of electrodes, means for applying electricpotentials to said electrodes, means for selectively impressing energyfrom said output circuit on said input circuit in aiding and opposingsenses with respect to the energy in said input circuit, and means forvarying the potential applied to one of said electrodes from one valuewhen said energy is coupled back in said aiding sense to another valuewhen said ener-gy is coupled back in opposing sense.

10. In signal responsive apparatus, an electric discharge device havinginput and output circuits including a plurality of electrodes, means forapplying electric potentials to said electrodes, means for selectivelyfeeding back energy from said output circuit to said input circuit inphase with and in phase opposition with the energy in said inputcircuit, said in phase feed back being of a magnitude sulicient to causesustained oscillations in said input and output circuits, and means forvarying the potential applied to one of said electrodes from one Valuewhen said feed back energy is in phase with the energy in said inputcircuit to another value when said fed back energy is in phaseopposition with the energy in said input circuit.

11. In signal responsive apparatus, an electric discharge device havinga cathode, a control grid and an anode, means for impressing inputenergy on said control grid, a load impedance connected to said anode, abias resistor connected to said cathode, a direct current source ofelectric energy having its positive terminal connected to the free endof said load impedance and its negative terminal connected to the freeend of said bias resistor, means for impressing a fraction of thealternating voltage between said anode and said cathode on a firstcontact member, means for impressing a fraction of the alternatingvoltage between said anode and said cathode on a second Contact memberwith a phase substantially opposing the phase of the voltage on saidnrst mentioned contact member, a third contact member selectivelyengaging with said rst mentioned and said second mentioned contactmembers, a return impedance connected at one end to said control gridand at the other end to said third contact member, and means forconnecting said other end of said return impedance to the negativeterminal of said source when said rst contact member and said thirdcontact member are in engagement, and to said cathode when said secondcontact member and said third contact member are in engagement. A

12. In radio transmitting apparatus, an electric discharge device havinga cathode, a control grid and an anode, said cathode being connected toground through a direct current impedance, a transformer having primaryand secondary windings, a connection between said primary Winding andsaid anode, a resistive impedance connected to said anode and to ground,means for impressing a portion of the voltage across said resistiveimpedance on a rst contact member, means connecting one terminal of saidsecondary winding to said cathode, a resistive impedance connectedbetween a second terminal of said secondary winding and said cathode,means for impressing a portion of the voltage across said secondmentioned resistive impedance on a second contact member, a thirdcontact member selectively engageable with said rst mentioned contactmember and said second mentioned contact member, a resistive impedanceconnected between said control grid and said third mentioned contactmember, and means for supplying electric energy to the anode circuit ofsaid `discharge device.

13. In radio transmitting apparatus, a first electric discharge devicehaving a cathode, a control grid and an anode, a two terminal source ofelectric energy, a switch and impedance connected in series between oneterminal of said source and said anode, means connecting said cathode tothe other terminal of said source, means for im- .pressing an inputsignal on said control grid, a second electric discharge device having acathode, a control grid and an anode, a transformer having a primary andsecondary winding, means connecting said primary winding between saidone terminal of said source and the second of said anodes, resistivemeans connecting the second of said cathodes to said other terminal ofsaid source, an impedance connected to the second of said anodes and tosaid other terminal of said source, means for impressing a portion ofthe voltage across said impedance on a first contact member, meansconnecting one terminal of said secondary winding to said other terminalof said source, an impedance connected between a second terminal of saidsecondary winding and the second of said cathodes, means for impressinga portion of the voltage across the second mentioned impedance on asecond contact member, a third contact member selectively engageablewith said lirst contactmember and said second contact member, animpedance connected between the second of said control grids and saidthird contact member, a capacitor connected between the rst of saidanodes and the second of said control grids, and means for operatingsaid switch synchronously with the operation of said third contactmember.

ROBERT J. DAVIS.

REFERENCES CKTED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,894,952 Gebhard Jan. 24, 19332,006,440 Chireix July 2, 1935 2,024,489 Van Der Pol et al. Dec, 17,1935 2,173,426 Scott Sept. 19, 1939 2,173,427 Scott Sept. 19, 19392,244,751 Werrmann June 10, 1941 2,289,752 Bruck et al. July 14, 1942Certicate of Correction Patent No. 2,439,844. April 20, 1948.

in the printed specification of the above It is hereby certied thaterrors appear sectmn numbered patent requiring correctx read section26,1'me 17, after the numero.

umu 9 line 24, for feed read jed; and that the sind occurrence insertdown; co1

hould be read wlth these correctlons therem that the same may con-Letters latent s d of the case in the Patent O ce.

form to the recor MSigned and sealed this 15th day of June, A. D. 1948.

THOMAS F. MURPHY,

Assistant ommssioner of Patents.

Certicate of Correction Patent No. 2,439,844. April 20, 1948.

in the printed specification of the above It is hereby certied thaterrors appear sectmn numbered patent requiring correctx read section26,1'me 17, after the numero.

umu 9 line 24, for feed read jed; and that the sind occurrence insertdown; co1

hould be read wlth these correctlons therem that the same may con-Letters latent s d of the case in the Patent O ce.

form to the recor MSigned and sealed this 15th day of June, A. D. 1948.

THOMAS F. MURPHY,

Assistant ommssioner of Patents.

Certificate of Correction Patent No. 2,439,844. April 2o, 1948.

ROBERT J. DAVIS It is hereby certified that errors appear in the printedspecification of the above numbered patent requiring correction asfollows: Column 5, line 14, for section 2 read section 26'; line 17,after the numeral 12 insert to; line 45, after key second occurrenceinsert down; column 9, line 24, for feed read fed; and that the saidLetters Patent should be read with these corrections therein that thesame may conform to the record of the case in the Patent Office.

Signed and sealed this 15th day of June, A. D. 1948.

THOMAS F. MURPHY,

Assistant om/mzss'ioner of Patents.

